Azalea leaf gall causes crusty leaves on your azalea

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Last Updated: 
February 19, 2003

CORVALLIS - Are you noticing swollen-looking leaves on your azalea? Are they enlarged, pale green, grayish or whitish colored and fleshy looking? Your plants may be suffering from azalea leaf gall.

"Azalea leaf gall is caused by the fungus Exobasidium, which causes the leaves and flowers to be transformed into swollen galls," explained Melodie Putnam, diagnostic plant pathologist for the Oregon State University Plant Clinic. "These galls stand out and draw the attention of gardeners and passers-by."

Expanding flower buds and leaves are the most susceptible, but the disease most commonly occurs on leaves, said Putnam. All or a portion of a leaf may be affected, becoming a swollen and disfigured gall.

"The fungus overwinters in bud scales, those overlapping tissues that cover and protect the buds," she continued. "It infects the young buds as they begin to expand in early spring. As the leaves or flowers grow larger, the fungus grows throughout the tissues, causing them to swell. As the season progresses, the fungus breaks through the surface of the galls and forms spores, making a white non- powdery surface over the gall.

The spores can be washed by rain down to expanding buds on the same or on nearby plants, causing other infections," she added. "But only young tissues are susceptible.

"The disease usually fluctuates in severity and incidence, depending on the weather," said Putnam. "The disease is more frequent in years with high humidity or when plants are rained on or irrigated from overhead during the period of leaf expansion. Plants in heavy shade and with poor air circulation are more likely to become diseased."

Fortunately azalea leaf and flower gall is primarily a cosmetic concern and is not a problem that adversely affects the health of the plant, according to Putnam.

"The best means of control is to pick off and destroy the galls before they turn white," she said. "Discarding in the garbage is the best way to get rid of the galls. Also, avoid wetting the foliage when watering to prevent disease development."

Author: Carol Savonen
Source: Melodie Putnam